1. Field of the Invention
The present invention relates to a lens barrel and an optical equipment, and more particularly to a lens barrel and an optical equipment that allow an automatic focusing operation by a vibration motor such as an ultrasonic motor and a manual focusing operation without any particular switching operation.
2. Related Background Art
FIG. 1 is a cross-sectional view of a conventional lens barrel.
In FIG. 1, there are shown an outer tube 501 of the lens barrel; a fixed tube 503 having an outer tube portion 503a positioned in front of the outer tube 501 and a helicoid forming portion 503b provided inside the outer tube portion 503a; a manual operating ring 504 fitted on a circumferential groove 503c formed on the external periphery of the outer tube portion 503a of the fixed tube 503 and on a circumferential groove 501a formed on the external periphery of the outer tube 501 and rendered rotatable about the optical axis Z of the lens L; and a lens holder 505 supporting the lens L and provided on the external periphery with a helicoid 505b engaging with a helicoid 503d formed on the internal periphery of the helicoid forming portion 503b of the fixed tube 503. The lens holder 505 is penetrated by a groove 505a extending parallel to the optical axis Z, and a lens holder driving arm 520, to be explained later, having a portion parallel to the optical axis Z is inserted in the groove 505a so as to be slidable only in the radial direction of the lens L.
A tubular member 502 is provided at an end thereof with an outward flange 502a connected by screws 522 with the rear end of the fixed tube 503 and, at the other end, with an inward flange 502b connected by screws 523 with the outer tube 501. On the external periphery of the tubular member 502, there are mounted all the components of an ultrasonic motor 530, an output member 531 in contact with a rotary ring 512 of the ultrasonic motor 530 and a manual operation force entering ring 516 for entering the operation torque of the above-mentioned manual operation ring 504.
In the following, there will be explained the components of the ultrasonic motor 530 and the structure of the output member 531.
The ultrasonic motor 530 is composed of an annular vibration member 506 (corresponding to a stator) having a trapezoidal cross section; an electrostriction element 507 physically adhered to an end face of the vibration member 506; an annular vibration absorbing member 510 composed, for example, of felt and pressed to the surface of the electrostriction element 507; a first annular spacer 509 positioned in contact with an end face of the vibration absorbing member 510; a first annular Belleville spring 508 for pressing the spacer 509 toward the annular vibration member; a first annular nut 511 fitted on a screw portion 502d formed on the external periphery of the tubular member 502; a rotary ring 512 constituting a part of the rotor of the ultrasonic motor 530; a rubber ring 513 for avoiding the transmission of axial vibration to the rotary ring 512; an annular circumferentially movable member 514; and a vibration member rotation-blocking member 515 fitted on the external periphery of the tubular member 502 and having an external rim projection 515a inserted in a groove 506a of the vibration member 506.
The rotary ring 512, the rubber ring 513 and the circumferentially movable member 514 are integrated to constitute the rotor of the ultrasonic motor 530, and a circumferentially traveling wave generated in the vibration member 506 causes the rotor, consisting of the rotary ring 512, the rubber ring 513 and the circumferentially movable member 514, to rotate about the optical axis Z.
The nut 511 is provided for adjusting the contact pressure between the vibration member 506 and the circumferentially movable member 514, by the adjustment of the elastic force of the Belleville spring 508.
An output ring 531 positioned adjacent to the end face of the rotary ring 512 (namely, the rotor) of the ultrasonic motor 530 is composed of a ring 519, rotatably fitted on the external periphery of the tubular member 502; roller support shafts 518 fixed in at least three positions on the periphery of the ring 519 so as to protrude from the external periphery thereof along radial axes perpendicular to the optical axis (axis of the ultrasonic motor); and hollow rollers 517 fitted on the roller support shafts 518.
The ring 519 also serves as the output member of a drive force generating unit 532 (including the ultrasonic motor 530 and the output ring 531), and an L-shaped lens holder driving arm 520, for rotating the lens holder 505, is fixed by a screw 521 to an end face of the ring 519.
The rollers 517 are in contact, at the external periphery thereof, with an end face of the rotary ring 512 and an end face of the manual operation force entering ring 516.
The manual operation force entering ring 516 is rotatably fitted on the tubular member 502 and is in contact, at an end face (at the right side in the drawing), with the external periphery of the rollers 517.
The external peripheral rim of the manual operation force entering ring 516 engages with a recess in the internal periphery of the manual operation ring 504, whereby the ring 516 is rotated by the manual operation ring 504.
The above-mentioned lens holder driving arm 520 is inserted, through a hole 502c penetrating the periphery of the tubular member 502, into the groove 505a of the lens holder 505. The hole 502c penetrating the periphery of the tubular member 502 is an oblong hole extending in the circumferential direction.
The above-mentioned rollers 517 constitute a differential mechanism, positioned between the manual operation force entering ring 516 for the manual focusing operation and the rotary ring 512 of the ultrasonic motor for the auto focusing operation. The differential mechanism uses the output side thereof for driving a focusing lens, whereby the structural feature of the ultrasonic motor is fully exploited, particularly in the manual focusing operation.
The full exploitation of the structural feature of the ultrasonic motor means that, due to a fact that the rotor featuring the ultrasonic motor is maintained in pressure contact with the stator, the non-rotating state of the rotor is constantly maintained by the frictional force between the rotor and the stator except when the motor is driven so that the motor input ring connected to the rotor is also maintained in the non-rotating state without requiring any particular structure.
In the above-explained differential mechanism, the pressure of the Belleville spring 508 maintains the non-rotating state of the manual operation force entering ring 516 even when the rotary ring 512 is rotated, and, in the case of a manual focusing operation by the rotation of the manual operation force entering ring 516, the non-rotating state of the rotor (512-514) of the ultrasonic motor is maintained, since the rotor is maintained in pressure contact with the stator, so that the auto focusing operation and the manual focusing operation can be switched without any switching mechanism.
In the conventional lens barrel explained above, rollers are employed in the planet mechanism in the differential mechanism for switching the manual focusing operation and the auto focusing operation without any converting operation, and the transmission of the driving force is achieved by maintaining these rollers in friction contact on both sides with the output end face constituted by the rotary ring of the ultrasonic motor and with the output end face constituted by the manual operation force entering ring. The pressure for such friction contact utilizes that of the pressurizing member of the stator of the ultrasonic motor and is so set as to balance the slip torques of the friction contacts of the above-mentioned rollers with the output end face of the ultrasonic motor and with the output end face of the manual focusing ring, in order to achieve efficient transmission of the output of the ultrasonic motor. For this reason, in the case of driving a focusing lens having a large driving load, there is generated a slippage in the friction contact with the rollers, whereby the output of the ultrasonic motor cannot be transmitted efficiently and the lens drive cannot be achieved in a satisfactory manner.